Rotational isomerism in 3,4-dimethyl-3,4-dinitrohexane

Abstract

I.r. and Raman spectra of 3,4-dimethyl-3,4-dinitrohexane (in the solid and solution states) are reported and assignment of frequencies made. It is assumed that the higher melting isomer has the meso- and the lower melting isomer the (±)-configuration. Comparison of the Raman and i.r. spectra of both the solid and solution states of meso-3,4-dimethyl-3,4-dinitrohexane shows that this compound exists in the gauche conformation in the solid state but as a mixture of gauche and trans rotamers in solution. Dipole moments in different solvents (benzene, carbon tetrachloride, and cyclohexane) at different temperatures and molar Kerr constants (in carbon tetrachloride and benzene) are also reported. Analysis of the dielectric data shows that at 25°C, meso-3,4-dimethyl-3,4-dinitrohexane exists as a rotameric mixture of 53%gauche and 47%trans in carbon tetrachloride solution, and 80%gauche and 20%trans in benzene solution. On the other hand, our spectral data suggest that in the solid state (±)-3,4-dimethyl-3,4-dinitrohexane exists as a mixture of the two possible rotamers in which the nitro groups are gauche to each other. In non-polar solvents like carbon tetrachloride, an additional rotamer, in which the nitro groups are trans to each other, appears. Analysis of the dipole moment data suggests that the combined proportion of the ‘gauche’ rotamers is 24% in carbon tetrachloride and 43% in benzene.